We make a mental note to run tests after future rebases and before force
pushes, for reflog is an option of last resort, like a union lawyer.

prune

Before we end our shift, we git remote prune origin:

- [deleted] 3159-fix-mobile-web

The manual explains:

Deletes all stale remote-tracking branches under origin. These stale branches
have already been removed from the remote repository referenced by origin,
but are still locally available in remotes/origin.

So, it looks like 3159 was merged in or deleted on origin by another teammate.